This invention relates to a refrigerator equipped with a two-stage compressor and two evaporators for performing a refrigeration cycle.
Such a refrigerator has been proposed and described in U.S. Pat. No. 4,918,942.
The refrigeration cycle of the prior art document comprises following steps; each of the steps will be explained by referring FIG. 8, which shows a refrigerant circuit 100.
(1) Gaseous refrigerant streams out at high pressure from an outlet of the two-stage compressor. Then, the gaseous refrigerant is condensed at interior of a condenser 14 to become a two-phase refrigerant composed of gas and liquid phases at high pressure.
(2) The two-phase refrigerant at high pressure is subjected to pressure reduction in a capillary tube 16xe2x80x2. Then, the two-phase refrigerant at intermediate pressure flows into an evaporator 18 for fresh food compartments or non-freezing refrigerator compartment (hereinafter referred as xe2x80x9cfresh food evaporatorxe2x80x9d).
(3) Liquid-phase part of the two-phase refrigerant partly evaporates at inside of the fresh food evaporator 18. Then, the two-phase refrigerant enters into a separator 20xe2x80x2, through which gas-phase and liquid-phase parts are separated from each other.
(4) Gaseous refrigerant that is separated from liquid refrigerant by the separator 20xe2x80x2 flows through a suction pipe 22 at intermediate pressure; and then returns to the two-stage compressor 12 through its intermediate-pressure side inlet.
(5) Liquid refrigerant that is separated from the gaseous refrigerant by the separator 20xe2x80x2 is subjected to pressure reduction at a throttle valve 114, to form a two-phase refrigerant at low pressure. Then, the two-phase refrigerant at low pressure flows into an evaporator 26 for freezer compartment (hereinafter referred as xe2x80x9cfreezer evaporatorxe2x80x9d).
(6) Liquid part of the two-phase refrigerant evaporates in the freezer evaporator 26. Thus formed gaseous refrigerant flows through a suction pipe 28 at low pressure; and then returns to the two-stage compressor 12 through its low-pressure side inlet.
The prior art refrigeration cycle has a problem of occasional occurrence of so-called xe2x80x9cone-sided flowxe2x80x9d and resulting interruption of cooling of the freezer compartment. The xe2x80x9cnone-sided flowxe2x80x9d means undesirable interruption of refrigerant flow in the freezer evaporator 26 while refrigerant continues to flow through the other passage in the refrigerant circuit. In other words, whole of refrigerant taken into the separator 20xe2x80x2 flows out to the suction pipe 22 at intermediate pressure, and then into the intermediate-pressure side inlet of the compressor 12. The xe2x80x9cone-sided flowxe2x80x9d occurs when a pressure balance between the fresh food evaporator 18 and the freezer evaporator 26 is lost. The xe2x80x9cone-sided flowxe2x80x9d does occur especially when heat-exchange temperature of the freezer evaporator 26 rises too high at occasion of excessive rise of temperature in the freezer compartment.
Meanwhile, at occasion of dropped room temperature in winter season or the like, no cooling at the fresh food evaporator 18 is needed while need of cooling at the freezer evaporator 26 still remains. The prior art refrigeration cycle also has a problem in such occasion. Because the fresh food evaporator 18 and the freezer evaporator 16 are connected in serial, refrigerant also have to flow through the fresh food evaporator 18.
The xe2x80x9cone-sided flowxe2x80x9d also occurs when an excessive cooling or heat exchange is made by the fresh food evaporator 18, because such excessive heat exchange makes liquid-phase refrigerant entirely evaporates in the fresh food evaporator 18 and thus exhausting the liquid-phase refrigerant that is in otherwise to be sent to the freezer evaporator 26.
First aspect of invention-wise refrigerator comprising: a two-stage compressor having an outlet and first and second inlets, pressure of said fist inlet being intermediate between pressures of the outlet at higher pressure and the second inlet at lower pressure; means for switching of refrigerant flow channels at downstream of a condenser connected with said outlet; means for separating gaseous and liquid phase parts of refrigerant from each other at downstream of a first evaporator for fresh food compartment, said first evaporator being connected from first exit of said means for switching through a first capillary tube; a first suction pipe connecting from a gaseous part exit of said means for separating to said first inlet of the two-stage compressor; a second capillary tube connecting from a liquid part exit of said means for separating to a second evaporator for freezer compartment; a bypass capillary tube connecting to the second evaporator from second exit of said means for switching; a second suction pipe connecting from the second evaporator to said second inlet of the two-stage compressor; and means for controlling a refrigeration cycle in a manner of bypassing or skipping the first evaporator when temperatures of said first suction pipe becomes lower than a predetermined value, by closing said first exit of the means for switching and by opening said second exit of the means for switching.
According to second aspect of the invention, said bypassing is made when temperature of the second suction pipe becomes higher than a predetermined value, alternative to that of the first aspect of the inventionxe2x80x94bypassing is made when the temperatures of said second suction pipe becomes lower than a predetermined value.
According to third aspect of the invention, said bypassing is made when temperature of the means for separating becomes lower than a predetermined value, alternative to those of former aspects of the invention.
According to fourth aspect of the invention, said bypassing is made when temperatures of the means for separating and the second evaporator being become substantially same, alternative to those of former aspects of the invention.
According to fifth aspect of the invention, said bypassing is made when drive frequency of a motor for operating said two-stage compressor increases to a predetermined magnification, alternative to those of former aspects of the invention.
According to sixth aspect of the invention, a fan for leading air around said first evaporator into the fresh food compartment is driven at a time of said bypassing by said means for controlling.
A normal mode of refrigeration cycle of the refrigerator is explained in below.
(1) Gaseous refrigerant streams out at high pressure from an outlet of a two-stage compressor, and is condensed in a condenser to form a two-phase refrigerant composed of gaseous and liquid phases.
(2) The two-phase refrigerant of high pressure is subjected to pressure reduction within a first capillary tube to become a two-phase refrigerant of intermediate pressure; and then flows into a first evaporator for cooling a fresh food compartment.
(3) Liquid part of the two-phase refrigerant partly evaporates in the first evaporator. Then, the two-phase refrigerant flows into means for separating gaseous and liquid parts of refrigerant from each other.
(4) Gaseous refrigerant that is separated from liquid refrigerant by the means for separating returns directly through a first suction pipe into the two-stage compressor from its first inlet. The first inlet is at an intermediate pressure between pressures at outlet and second inlet of the two-stage compressor.
(5) Liquid refrigerant that is separated from the gaseous refrigerant by the separator flows through a second capillary tube as being reduced in pressure to become a two-phase refrigerant; then the two-phase refrigerant at lower pressure flows into a second evaporator for cooling a freezer compartment.
(6) Liquid part of the two-phase refrigerant evaporates in the freezer compartment. Thus formed gaseous refrigerant returns, through a second suction pipe at pressure lower than that of the first suction pipe, into the two-stage compressor 12 from its second inlet.
The invention-wise refrigerator operates not only in normal mode but also in xe2x80x9cbypassingxe2x80x9d mode of refrigeration cycle as in below.
According to the first aspect of the invention, occurring of xe2x80x9cone-sided flowxe2x80x9d is assumed when temperature of the first suction pipe exceeds a predetermined temperature. In such occasion, the first exit of the switching means is closed while the second exit of the switching means is opened, thereby bypassing refrigerant directly to the second evaporator for the freezer compartment while skipping the first evaporator for the fresh food compartment. In this way, the xe2x80x9cone-sided flowxe2x80x9d is prevented or quenched by directly providing refrigerant to the second evaporator, and thus cooling of the freezer compartment being effected.
According to the second aspect of the invention, the xe2x80x9cone-sided flowxe2x80x9d is detected by temperature of the second suction pipe, pressure in which is lower than that of the first suction pipe. Meanwhile, the xe2x80x9cone-sided flowxe2x80x9d is detected by: temperature of the separating means in the third aspect of the invention; by temperature difference between the separating means and the first evaporator in the fourth aspect of the invention; by drive frequency of a motor for operating the two-stage compressor in the fifth aspect of the invention.